Rice is a high starch, low protein grain that is a staple item of diet for many parts of the world. Rice is composed of about 80% carbohydrate with about 6-10% protein. The rice protein has a relatively high PER (protein efficiency ratio--ratio of weight gain of rats to protein consumed) of about 2.18 which is almost equivalent to that of beef (2.30), a considerably more costly protein source. However, because of the sheer bulk involved, children and infants cannot eat a sufficient amount of rice to meet daily protein requirements. Moreover, rice protein is insoluble which makes feeding rice-based formula to young infants difficult.
Efforts to improve the protein level in rice involving selective breeding of new rice varieties have increased protein levels somewhat but not to the extent of providing strains with protein levels suitable for use in rice-based infant formula. Another approach has been to increase the protein content of rice flour by gelatinizing and enzymatically digesting rice starch with carbohydrate degrading enzyme commonly known as amylases. This treatment hydrolyzes the starch to soluble saccharides of various molecular weights such as glucose, maltose, oligosaccharides, and dextrins from which the insoluble protein-enriched rice flour is separated, for example by centrifugation. Thus, by partial removal of solubilized carbohydrate, the protein content of the processed rice flour is correspondingly enhanced to provide what is referred to herein as high protein rice flour (HPRF). Prior art within this general area includes the following papers.
Hansen, et al., Food Technology, 35 (No. 11), pages 38-42 (1981) developed a high protein rice flour (25% protein content) by using the enzyme alpha-amylase to digest the starch material of milled broken rice thereby decreasing starch content resulting in increased protein content compared to the original rice flour. In the Hansen, et al. process, a 5% slurry of finely ground crude rice flour is first heated for 30 min. at 100.degree. C. to effect gelatinization, then partially digested by enzyme (alpha-amylase) treatment, centrifuged and the insoluble HPRF freeze-dried. Protein level of HPRF was reportedly increased three-fold over the starting material (approximately from about 8% to 25%). The supernatant is principally carbohydrate (98.3%).
Chen, et al., J. Sci. Food Agric. 35, 1128-1135 (1984) modified the Hansen et al. process to provide both HPRF and high-fructose rice syrup from broken rice. In the Chen, et al. process, a 20% slurry of the milled broken rice is mixed with calcium chloride (70 mg/kg rice), pH adjusted to 6.5 and digested (liquified) with alpha-amylase optimally at 90.degree. C. for 90 minutes. Specifically, Termamyl 60L alpha-amylase obtained from Novo Industri, A/S, Denmark, is employed. The liquified mixture is centrifuged and the insoluble HPRF dried. Protein content of the HPRF was similar to Hansen, et al. (approximately three times as high as the raw material). The supernatant is saccharified at 60.degree. C. with glucoamylase and then isomerized to fructose with glucose isomerase to provide a high-fructose rice syrup containing 50% glucose, 42% fructose and 3% maltose.
Chang, et al., Journal of Food Science, 51 (No. 2), pages 464-467 (1986) further modified the Hansen, et al. process to produce a rice flour with increased protein and calcium contents. According to Chang, et al., processing conditions for the production of HPRF concerned treating gelatinized rice flour slurry with calcium chloride and alpha-amylase at 60.degree. C. for 90 min. The hydrolyzed starch is removed by centrifugation and the insoluble paste freeze dried to yield high protein rice flour with approximately 38% protein, a PER ratio of 2.17 and an amino acid composition similar to the rice flour of Hansen, et al.
The enzymatic hydrolysis of rice starch has also been investigated in connection with developing rice syrup sweetener and rice-milk as noted in the following publication and Mitchell, et al. patents.
Griffin, et al., Journal of Food Science, 54 (No. 1), pages 190-193 (1988) studied processing modifications required to provide high yields of liquified rice starch from milled rice using heat-stable alpha-amylase and a starting solids content of 30% with the conclusion that rice maltodextrins could be most effectively produced at a processing temperature of 80.degree. C.
Mitchell, et al., U.S. Pat. No. 4,744,992 describes the production of a nutritional rice milk product obtained by liquifying whole grain rice particles with alpha-amylase enzyme followed by saccharification with a glucosidase enzyme. The process does not enhance protein content and minerals found in the whole grain rice are retained.
Mitchell, et al., in a related patent (U.S. Pat. No. 4,756,912) partially clarified the saccharification product of U.S. Pat. No. 4,744,992 to remove substantially all rice fiber while leaving substantial portions of all other nutritional components to produce a rice syrup sweetener.
High protein rice flour obtained as described in the prior art has not proved to be satisfactory with respect to use in infant formula. Over 80% of rice protein consists of glutelin which is completely insoluble at pH's generally considered acceptable for infant formula. As a result, formulas made with such protein do not form satisfactory dispersions, have a very grainy, gritty mouthfeel and tend to plug up the nipple.
The prior art noted above principally concerns the production of HPRF and/or rice syrup sweeteners. There are no teachings regarding removal or reduction of phytic acid or undesirable minerals, such as manganese, selenium and aluminum, which are concentrated in the final product during processing of the rice raw material or to provision of solubilized rice protein suitable for sterilized ready-to-use (RTU) formula.
With regards to aluminum, this mineral is present throughout the food chain and it is known that foods of plant origin, including rice, contain higher concentrations of aluminum than bovine or human milk.
Infants with normal kidney function absorb very little dietary aluminum and consequently the amount of aluminum present in infant formula does not appear to present problems. Aluminum that is absorbed is excreted efficiently by the kidneys in these infants. However, patients with impaired kidney function or premature infants with immature kidney function are considered at higher risk of developing aluminum-associated metabolic disorders, including bone disorders, because of a lower than normal ability to excrete systemic aluminum via the kidneys.
Thus, infants at greatest risk of aluminum toxicity include those with impaired renal function, prolonged requirement for parenteral nutrition, and preterm infants with increased need for calcium and phosphorus. An infant formula with reduced aluminum content is preferred for these infants.
With regards to selenium, toxic effects of this mineral in animals and man from excessive intakes were known long before its nutritional effects. As to the latter, selenium is now recognized as an essential trace mineral in both animals and man. Two human selenium deficiency diseases have been described and studied in the People's Republic of China, Keshan and Kaschin-Beck disease. The margin of safety between deficiency and toxicity for selenium intake is narrower than for most other trace elements.
Food constituents are the main source of selenium either through plant or animal protein sources. In general, the food intake of selenium in different parts of the world falls within the range of 20 to 300 mcg per day. The selenium intake of infants is of particular interest because of their rapid growth and increased metabolic requirements. The estimated safe and adequate daily dietary intake of selenium is shown below.
______________________________________ Estimated Safe and Adequate Daily Dietary Intake Range of Selenium* mcg Daily Age Group (Years) Selenium Intake ______________________________________ Infants 0-0.5 10-40 0.5-1.0 20-60 Children 1-3 20-80 4-6 30-120 Adolescents & Adults 50-200 ______________________________________ *U.S. National Academy of Sciences, National Research Counsel (1980), Recommended Dietary Allowances, Food and Nutrition Board, Committee on Dietary Allowances, Washington, DC, p.195.
The amount of selenium in rice is dependent on the region where it is grown. Thus, it is prudent to generally reduce the levels in processed rice used for the preparation of infant formula. The process technology for the preparation of soluble rice protein described in this patent application provides about a 25-30% reduction in the amount of selenium associated with the protein thereby minimizing the risk of the selenium content being higher than the recommended safe and adequate range.
Phytic acid (hexaorthomonophosphate ester of myo-inositol) is the principal storage form of phosphate and is ubiquitously distributed in plants, particularly in cereal grains (including rice) and legumes. It is known that under certain conditions, phytic acid in the diet may decrease the absorption of dietary minerals such as zinc, calcium, magnesium and iron.
Phytic acid is not present in human milk or cows milk based infant formula but is found in soy-based formula. Lonnerdal, et al., Am J Clin Nutr 1988; 48:301-6, showed that low bioavailability of zinc from soy formula compared to cow milk formula is a function of its phytic acid concentration and can be overcome by the removal of phytic acid.
Since the phytic acid content of rice is nearly as high as soy on a protein basis, it is important to reduce the phytic acid level of rice-based infant formula. However, the prior art has not addressed the problem of phytic acid reduction in rice flour processing. The process technology for the preparation of soluble rice protein described in this patent application reduces the phytic acid content to extremely low levels.
With regards to manganese, applicants' Puski, et al. U.S. Pat. No. 4,830,861 patent which issued May 16, 1989 (incorporated herein by reference) describes a process for preparing HPRF with safe and adequate manganese levels for infants from commercially available rice flour which typically contain about 150-260 micrograms (mcg) manganese per gram protein.
In the conventional prior art processes involving gelatinization and enzymatic digestion of rice flour, along with increased protein content there is a concomitant enrichment of manganese to a level substantially greater than what is considered safe and adequate for daily dietary intake. Apparently, the manganese associates with the protein and remains with the separated HPRF rather than the solubilized saccharides.
While manganese is considered an essential element in the mammalian diet, it is also known that only relatively small quantities are required by human infants. Human milk levels are generally below 32 micrograms per quart and pediatric nutritionists favor infant formula with relatively low manganese levels. The National Academy of Sciences-Food and Nutrition Board (NAS-FNB) has determined the U.S. average daily intake and the estimated safe and adequate daily dietary intake as follows.
______________________________________ Dietary Intake U.S. Avg. Daily Intake ______________________________________ Infants 10-300 mcg/day Children, 3-5 yrs. 1,400 mcg/day Children, 10-13 yrs. 2,180 mcg/day Adults 2,500-9000 mcg/day ______________________________________ Estimated Safe and Adequate Daily Dietary Intake ______________________________________ Infants 0-6 months 500-700 mcg/day Infants 6-12 months 700-1000 mcg/day Children and Adolescents 1,000-3,000 mcg/day Adults 2,500-5,000 mcg/day ______________________________________
A quart of infant formula typically contains about 14-20 g protein. As previously mentioned, the HPRF of the prior art retains substantially all of the manganese present in rice flour which has typical manganese levels of 150-260 micrograms per gram protein. Thus, the amount of manganese in a quart of rice protein based infant formula containing 14 and 20 grams protein is calculated as follows for particular levels of rice flour manganese.
______________________________________ Manganese Per Quart Formula From Rice Flour (grams protein .times. mcg manganese per gram) Manganese Content of Rice Flour Micrograms Manganese per Quart (mcg/g Protein) 14 g protein/qt. 20 g protein/qt. ______________________________________ 150 2100 3000 260 3640 5200 ______________________________________
With the assumption that an infant's diet includes one quart of formula per day, rice flour as a source of protein can contain a maximum of about 50 mcg of manganese/g protein (estimated maximum safe and adequate daily dietary manganese intake of 700 mcg/day for infants 0-6 months divided by 14 grams of protein). Consequently, rice flours cannot be used to make HPRF suitable for infant formula without reduction of manganese since they contain considerably more manganese as illustrated in Table I below.
TABLE 1 ______________________________________ Manganese Content of Commercial Rice Flours Source Manganese, mcg/g Protein ______________________________________ Riceland Foods.sup.a 150-163 California Rice Growers 150-200 Association.sup.b Riviana Rice Flour.sup.c 150-250 Coor's rice flour.sup.d 220-260 ______________________________________ .sup.a Stuttgart, AR .sup.b Sacramento, CA .sup.c Houston, TX .sup.d ADM Milling, Rice Div., Weiner, AR
The process of Puski, et al., U.S. Pat. No. 4,830,861 provides HPRF with substantially reduced manganese by:
(1) blending rice flour and water at a pH of 3.4 to 4.6, PA1 (2) separating the insoluble washed rice flour, PA1 (3) resuspending the washed rice flour and adjusting to a pH suitable for an alphaamylase enzyme, PA1 (4) treating with an alpha-amylase enzyme for a sufficient time to hydrolyze the starch to about 5-50 dextrose equivalents (DE), PA1 (5) adjusting mixture to pH of 3.4-4.6, PA1 (6) separating the rice syrup from the insoluble low manganese HPRF. PA1 (7) treating the low manganese HPRF with a proteolytic enzyme to hydrolyze 1 to 5% of the peptide bonds, PA1 (9) inactivating the enzymes with heat at 70.degree.-80.degree. C. PA1 digesting a slurry of the raw material with an alpha-amylase enzyme to solubilize the rice starch; PA1 heating the rice slurry at elevated temperature; PA1 separating the solubilized rice carbohydrate from the insoluble rice protein; PA1 treating a slurry of the insoluble rice protein with a protease enzyme; and PA1 separating the soluble rice protein from the insoluble rice material to provide a soluble rice protein concentrate with improved digestibility and low manganese, aluminum, selenium and phytic acid content. PA1 a protein content greater than 16%, preferably 16 to 90% protein on a solids basis, PA1 a manganese content 50 micrograms or less per gram protein, PA1 an aluminum content less than 15 microgram per gram protein, PA1 a selenium content reduced a minimum of 25% on a protein basis relative to the starting rice raw material, PA1 a phytic acid content less than 15 mg per gram protein and preferably less than 5 mg per gram protein, and PA1 a protein digestibility of greater than 90%.
The insoluble low manganese high protein rice flour is suitable as a basic ingredient for foodstuffs but further processing is required to provide dispersibility and mouthfeel characteristics appropriate for use in infant formula. This is carried out by:
The protease treated low manganese HPRF is spray dried to provide a modified HPRF containing 50 mcg or less manganese per gram protein. This relatively insoluble low manganese HPRF is suitable for powdered infant formula but cannot be used to make sterile liquid infant formula products. When retorted formula was prepared with low manganese HPRF, the resulting product was very grainy with a gritty mouthfeel after sterilization and poor storage stability which resulted in an unacceptable shelf life.
It is generally known in the art that rice protein is relatively insoluble in aqueous solutions. It is also common knowledge that digestibility of rice flour is low compared to milk protein or soy protein isolate. This may be due to the low solubility of rice protein. A reliable "in vitro" method for determining digestibility of rice protein was published by Bradbury, et al. (1984) Br. J. Nutr. 52: 507-13. The first step of this technique is digestion by pepsin at pH 1.5 at 37.degree. C. for 3 hours. The second step is digestion with a mixture of pancreatic enzymes at pH 8.2 at 37.degree. C. for 16 hours. Using this procedure, cooked rice had an "in vitro" digestibility of about 77%. MacLean (1978) J. Nutr. 108: 1740-47 demonstrated that apparent nitrogen digestibility in children 12-18 months old ranged from 52-78% with cooked rice. Thus, it is evident that cooked rice, as measured by "in vitro" and "in vivo" techniques, has low digestibility. With respect to rice in infant formula or nutritional products, a highly digestible rice protein is desirable and provision thereof is provided by the instant invention.